Understanding the metabolism, pharmacokinetics and pharmacodynamics of nicotine and other tobacco alkaloids will help define factors influencing smoking and its adverse effects and may lead to novel treatment approaches for tobacco addiction. We continue a research program combining synthetic and analytical chemistry and clinical investigation. Chemistry studies will include (a) developing methodology for quantitative analysis of tobacco alkaloids and metabolites and applying these methods to qualitatively and quantitatively define pathways of metabolism in humans. Particular emphasis will be placed on trans-3'-hydroxycotinine, which appears to be the major urinary metabolite of nicotine; (b) synthesis of tobacco alkaloids and stereoisomers, metabolites and deuterium-labeled analogs for pharmacologic and metabolic studies, and (c) developing GC-MS assays for nicotine metabolites and other tobacco alkaloids. Clinical studies will pursue extensions of the hypothesis that habitual smokers regulate body levels of nicotine; namely, (a) the rate of nicotine metabolism is an important determinant of individual differences in tobacco smoking behavior, and (b) administering nicotine in adequate levels or inhibiting nicotine metabolism will suppress self-determined intake of nicotine form smoking. Using stable isotope methodology, the kinetics of nicotine and cotinine, including measurement of percent conversion of nicotine to cotinine, and its relationship to daily intake of nicotine from smoking will be compared in men and women, young vs. old and smokers vs. nonsmokers. We will examine the influence of cigarette smoking per se on metabolism of nicotine. We will test the hypothesis that nonsmokers have significant response to nicotine at blood levels comparable to those seen after environmental tobacco smoke exposure. The influence of prolonged infusions of nicotine, dosed to fully replace levels of nicotine achieved by smoking, and of oral nicotine on daily intake of nicotine from smoking will be examined. The metabolism, kinetics and effects of (R)-nicotine, nornicotine and other tobacco alkaloids will be studied to see if these contribute to overall effects of cigarette smoking or interact with the metabolism or effects of natural (s)-nicotine. We will test whether (R)-nicotine influences smoking behavior and resultant effects. The proposed studies will clarify factor determining tobacco consumption and effects and may lead to more effective ways of treating tobacco addiction.